Rocks Igneous, Metamorphic, Sedimentary

What is a Rock?  A rock is a mixture of minerals, mineraloids, glass and organic matter.  Common minerals found in rocks include: feldspar, hornblende, and mica.  Granite is a mixture of these minerals.

Rock Cycle  There are three types of rock:  Igneous – formed by melting and cooling magma and lava.  Sedimentary – formed by weathering and erosion  Metamorphic – formed by heat and pressure over time.  Rocks change over time.

Igneous Rocks  Molten or liquid material from a volcano or from deep inside the Earth, cools to form igneous rocks.  Magma – High temperatures and high pressure deep in the Earth cause rocks to melt and form hot magma.

Earth’s Interior 

Earth’s Interior: Temperatures 

Igneous Rocks  At 60 to 200 km below the Earth’s surface the temperatures reach 1400 o C. (2550 o F)  Magma rises because it is less dense than the surrounding solid rock.

Igneous Rocks  Lava is magma that reaches the surface. Ropeypahoe lava

Igneous Rock: Intrusive Rocks  These are igneous rocks that form below the Earth’s surface.  They have large mineral grains.  Examples : Gabbro  Diorite

Igneous Rocks:Extrusive  These rocks are formed quickly when lava cools on or near the Earth’s surface.  Air and Moisture causes lava to cool quickly.  The quick cooling does not allow large crystals to form.  Extrusive rocks have a fine-grained structure.

Igneous Rocks: Extrusive Examples  Rhyolite  Obsidian

Igneous Rocks: Extrusive  Scoria - formed from gassy lava, it has air-pockets that give it a spongy appearance.  Pumice: Lava “foam”, some samples float in water.

Volcanoes  Pompeii, Italy WebWeb

Igneous Rocks: Vocabulary  Mafic – composed of ferromagnesian minerals- olivine, pyroxene, and amphibole. These are oceanic. The water cooled them quickly.  Felsic – composed of mostly quartz and feldspar. These are continental, cooling on dry land.

Igneous Rock  Aphamitic – texture, made of crystals too small to be seen without a microscope.  Porphyritic – rocks with two cooling rates, They have a mix of large and small crystals.  Porphyritic = look like chocolate chips! cookiescookies

Igneous Rocks: Vocabulary  Vesicular – gassy when formed, the rocks look like sponges.

Igneous Rocks Texture – Cooling Rate – Crystal Size – Description - Type  Vesicular -fast- none - air bubbles – extrusive  Glassy – fast – none - very smooth – extrusive  Aphanitic –quick–microscopic –fine grained - extrusive  Granitic – slow – visible – coarse grained - intrusive  Porphoritic – slow/then quick – small&large – Chocolate chip - Intrusive

Mineral Composition of Igneous Rocks Name – Minerals – Color – Density- Crustal Formation  Felsic – K-Feldspar, muscovite, quartz – Light – Low density – Continental  Intermediate- Hornblende, biotite, Na-plagioclase – Medium – Medium density – Continental/Ocean  Mafic – Olivine, Augite, Ca-plagioclase – Dark – High density - Oceanic